Yeah, as far as thaumaturgy goes, it only breaks the system if you let it. I've already spelled out before that in my games, if someone tries a munchkin ritual, first, I'll warn him in game. Then, I'll interrupt him in game. Finally, the roof will cave in and he will be devoured by Godzilla. Sponsored Magic is fine, so long as you keep in mind that you can only do some things.
EDIT: As far as just buying more and more in the way of powers, tell them they should get some Stunts. I mean, Stunts when used correctly give great boosts, and more flavor.